Igniter



Feb. 10, 1953 P, ATU 2,627,810

IGNITER Filed Oct. 27, 1945 INVENTOR JOHN P. CATL/N Patented Feb. 10, 1953 IGNITER John P. Catlin, Fairfield, Conn.,

mesne assignments, to the United States America as represente Navy assignor, by of d by the Secretary of the Application October 27, 1945, Serial No. 625,089

2 Claims.

This invention relates to an improved igniter for combustible mixtures and has a particularly valuable application to the ignition of the combustible mixture in the combustion pot of an automobile torpedo. A common form of automobile torpedo employs a turbine adapted to be driven by the expansion of an elastic fluid in the well-known manner. The elastic fluid fed to such a turbine is normally a mixture consistin of the products of combustion of a hydro-carbon fuel burned in a compressed air atmosphere. Water is customarily injected into the combustion pot to aid in controlling the combustion, and by its conversion into steam and subsequent expansion aids in driving the turbine. Ordinarily, the release valves which start the flow of these fluids to the combustion pot are operated on the release or launching of the torpedo and usually a similar valve applies compressed air to the operation of an igniter connected into the co nbustion chamber.

When the starting valves are first actuated, the mixtures of these fluids have not stabilized to uniform values, and if the fuel is ignited immediately, it may burn erratically or even refuse to burn at all. It is, therefore, a relatively common practice to delay the operation of the igniter until after the flow of air and fuel has continued long enough to have reached a condition of relative stability.

It will be appreciated that there are manifest advantages in an igniter which could be put into operation by the actual delivery of components of the combustible mixture to the combustion pot and which would burn thereafter for a Sllfiicient length of time to absolutely insure that the mixture was thoroughly ignited and stable combustion established.

It is an object of this invention to: provide an igniter which is directly responsive to predetermined pressure increases in the chamber to which the igniter is connected.

It is a further object of this invention to provide a torpedo igniter which is capable of mass production on an economical basis and one which, partly by reason of the uniformity essential to mass production, gives uniformly reproducible functioning.

An additional object is to provide an igniter of such simple mechanical design as to allow the major percentage of the bulk available for an igniter .to be used for the loading of the pyrotechnic elements which actually ignite the fuel.

. This invention contemplates the provision of a diaphragm actuated percussion firing mechanism for the igniter and contemplates applying directly to the diaphragm the back pressure produced by the admission of air and fuel to the combustion pot.

The exact nature of a preferred form of the invention as well as other objects and advantages thereof will more clearly appear from an inspection of the drawing, which is a longitudinal sectional view through a preferred form of the igniter.

Referring to the drawing by characters of reference, it may be seen that the igniter comprises a body I threaded as at 2 for insertion into a combustion pot and provided with a sealing flange 3. This body is adapted to be inserted open end first into the combustion pot of the torpedo with the inner or open end in communication with the interior of the pot and with the sealing flange 3 compressing a suitable gasket. The inner end of the body I is internally threaded to receive an end cap 4 which presses upon the edges of and secures in place the diaphragm 5. A spacer B separates the diaphragm from the cartridge 1 and serves to hold in place the paper protective disk 8.

The cartridge 1 is of such diameter as to permit ready insertion or removal from the body I and contains the pyrotechnic charges which have been consolidated therein by the application of a suitable amount of pressure. The exact composition of the charges forms no part of the present invention and the needed properties will be readily apparent to the skilled pyrotechnist. As an illustration, these charges may include a main burning charge 9 which is capable of producing a hot flame of considerable duration and in contact therewith an ignition mix IB which is capable of consistently igniting the main charge 9. The ignition mix I0 is compressed to form a relatively rigid body and has pressed into a depression in its end surface a pellet of stab primer mixture H. The primer mixture is readily ignitable when pierced by a suitable point and is itself capable of readily igniting the ignition mix It. As has been previously noted, the charges are protected by the application of the paper disk 8 and they may be additionally protected by the application of lacquer or other suitable moistureproofing agent to their end surfaces.

One or more vent grooves l2 are preferably provided in the end surfaces of the cartridge 1 to give any gases which may have been emitted by the pyrotechnic elements during storage a free access to the small annular space surrounding the cartridge and spacer 6. Since only slight decomposition of these charges may be expected even when stored for long periods of time under adverse conditions, the rate of evolution of such gases will be relatively low. Such gases as are evolved will escape through the threads retaining the cap 4 without permitting an appreciable increase in pressure within the body. At the same time, the passage is sufficiently restricted and tortuous that on exposure of the body to high external pressure there can be only a small entry of pressure into the body prior to the firing of the igniter.

The end cap 4 is provided with oneor more protection pins 13 which are adapted to protect the diaphragm 5 from mechanical injury. To insure that the cap i will not be inadvertently removed, it may be sealed in place as by application of a dot of solder Id.

The diaphragm 5 is of concave-convex form and is mounted with its convex surface presented to the outside or open end of the body. Centrallymounted in the diaphragm is a firing pin :5 which extends through an aperture in the diaphragm and is headed over upon a washer it. The diaphragm is centrally stiffened by the connection to the firing pin and uniformity of functioning is insured by this stiffening. To assist in centering the diaphragm and to insure that it is tightly gripped, the outer face of the spacer 6 is counterbored at I'i to receive the diaphragm. The end of the cap 4 is suitably formed to engage the diaphragm and the counterbore.

To assist in the removal of the cartridge for reloading, the body I is pierced at its closed end and the opening filled with a threaded set screw [9. To complete sealing at this point and to avoid loss or inadvertent removal, the set screw may be sealed in place by the application of solder 20.

In the utilization of my improved igniter with naval torpedoes, it is inserted into the combustion pot of the torpedo and secured therein with the flange 3 drawn up securely against a suitable lead Washer or other gasket. As is well known, the operation of the starting valve allows compressed air to enter the combustion pot and at substantially the same time feeding of the hydro-carbon fuel is commenced. Pressure in the combustion pot rises rapidly and may reach values of several hundred pounds per square inch. The curvature, thickness, and elastic modulus of the diaphragm are so chosen by reference to considerations to be discussed later that at a pressure of about 150 pounds per square inch the diaphragm becomes elastically unstable and deforms inwardly with a violent snapping action, completely reversing its curvature and driving the firing pin into the sensitive primer mix which is imbedded in and supporting the igniton charge. Prior to firing, the diaphragm acts as an end seal to substantially close the open end of the igniter but on firing, the heat of combustion and the evolution of gas from the pyrotechnic charges cause the diaphragm and firing pin to melt and blow into the combustion pot, The diaphragm and firing pin are both made of material which disintegrates rapidly at the high temperature reached by the pyrotechnic charges and by the fuel in the combustion pot. It is thus rendered certain that the nozzles or blading of the turbine will not be clogged or injured in any way.

The pressure required to snap the diaphragm is a function of several variables including:

1. Metal thickness. 2. Radius of curvature. 3. Youngs modulus of the metal employed. 4. Diaphragm diameter.

The yield point and ultimate strength of the material do not seem to have much bearing on the snapping pressure. This is borne out by tests on aluminum diaphragms in the annealed and in the half hard condition. Both tests gave practically identical snapping pressures. The elastic modulus seems to be more of a governing factor than the yield strength and it is well known that in many problems of elastic stability, the critical buckling load is not a function of yield strength.

The radius of curvature of the diaphragm has an important bearing on the snapping pressure. If the radius of curvature is too small, i. e., if the diaphragm has too deep a dome it will not deform properly when snapping, and the crtical pressure will vary widely. On the other hand, a diaphragm that has an extremely large radius of curvature does not give a violent enough blow to set on the primer mixture. In this case the movement of the diaphragm is small and great care must be used in maintaining proper spacing between the end of the firing pin and the primer surface. Using an effective diaphragm diameter of .625", a radius of curvature between .800" and 1.000 seems to give good results. A diaphragm of aluminum .008" thick and having a radius of curvature between these values will consistenly snap at 1501-30 p. s. i. Aluminum seemed to be the best diaphragm material of all those tested. It has a fairly low melting point and is not subject to creep or cold flow under the clamping pressure of the front cap.

Obviously, the diaphragm thickness has an important elfect on the critical snapping pressure. To secure uniformity, the aluminum sheet used for diaphragms should be held closely in thickness.

Zinc has been found suitable as a material for the firin pin. It has sufiicient hardness to penetrate the primer mixture, yet it has a low enough melting point to disintegrate readily in the combustion pot. A sharp point is preferable on the firing pin end to insure sensitivity.

As previously noted, the reinforcement of the center of the diaphragm by the washer and shoulder on the firing pin exerts an important effect on certainty of functioning. With the centrally reinforced diaphragm, it was found that the deformation was so uniform that the diameter of the primer composition could be reduced considerably below that thought necessary in the first experiments without sacrificing the reliability of performance.

Since torpedoes are always given one or several calibration runs and are frequently run in practice maneuvers, the fact that this igniter may be conveniently recharged is of considerable economic importance. To recharge this igniter, it is only necessary to take out the end cap and remove the old cartridge. The insertion of a new cartridge and a new diaphragm and firing pin assembly makes the igniter body ready for re-use. As previously noted, in the event a discharged cartridge resists removal, the set screw I 9 may be removed and the cartridge pushed out with a suitable instrument.

. .ns noted'above, vents have been provided to allow any gases which mayhave been evolved during storage to escape at a relatively slow rate from the body. This makes it certain that there can be no pressure built up during storage which might act against the diaphragm and cause it to resist the normal snapping action. However, when the diaphragm is exposed to the relatively fast increase of pressure within the combustion pot, there can be only a relatively slight leakage to the interior of the igniter body before the pressure has risen to an extent sufiicient to snap the diaphragm to a position of reversed curvature.

It is to be understood that the form of the invention herein specifically shown and described is intended only to be illustrative of the preferred embodiment and that various changes and reconstructions may be resorted towithout departing from the spirit of the invention as defined in the claims following.

I claim:

1. An igniter for combustible fiuid in a combustion pot to which said fluid is admissible under pressure, said igniter comprising a tubular body closed at one end excepting for an opening bisecting the circular wall of its bore and having an open end fitted into the wall of the pot for access of the pressure fluid, a powder-loaded and primed cartridge fitting the bore of the body and extending inwardly of the open end to define a chamber, a tubular spacer in the bore abutting the cartridge, a hollow cap driven into the open end toward the spacer, and a diaphragm clamped between the spacer and the hollow cap, said diaphragm being collapsible with a snap action by fiuid pressure in the combustion pot, a firing pin carried by the diaphragm to fire said loading upon 3 occurrence of the snap action, and a plug driven into said opening to close the bore, being remov- 5 pressure, said igniter comprising a tubular body with a bore closed at one end and having an open end fitted in the wall of the pot for access of the pressure fluid, a powder-loaded and primed cartridge in the bore, abutting the closed end of the body, a tubular spacer abutting the cartridge and being annularly spaced from the bore, a hollow cap in tandem with the spacer, being driven into the open end of the bore and having a diaphragm clamped between it and the spacer to define an inner chamber next to the cartridge, and a firing pin carried by the diaphragm and confronting the cartridge in the inner chamber to detonate the powder upon an inward snap action of the diaphragm by the pot fluid pressure, said cartridge having at least one vent communicating with the space around the spacer to provide egress for gas evolved by any decomposition of the powder prior to its detonation.

JOHN P. CATLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IENTS Number Name Date 927,434 Shonnard et a1 July 6, 1909 1,068,594 Leavitt July 29, 1913 5 1,385,610 Flam July 26, 1921 1,559,822 Wiley Nov. 3, 1925 2,405,932 Alderman Aug. 20, 1946 

